The overall objectives of this project are to study important aspects of heart cell contraction using a multidisciplinary approach. Specifically, we have observed that contractions of interconnecting myocyte cultures prepared from fetal rat hearts are arrested upon the addition of dibutyryl cyclic AMP. These arrested contractions are restored by either diluting the dibu cAMP from the culture medium or by addition of the microtubule inhibitor, colchicine. In addition, ultrastructural studies indicate that in dibu cAMP treated cells, the intercellular distribution of microtubules is altered. Based on these initial observations, the specific objectives of this proposal are to analyze the relationship between microtubules and contractility in heart cell cultures. In addition, using monospecific antibodies directed against tubulin, actin, and intermediate filaments, we plan to analyze the distribution of these fibrous proteins on cardiac cultures after various treatments using techniques of indirect immunofluorescence.